1. Field of the Invention
The present invention relates to a process for purifying an aqueous solution of hydrogen peroxide, and more particularly to a process for purifying an aqueous solution of hydrogen peroxide which provides a high purity aqueous solution of hydrogen peroxide used in the field of production of semiconductors.
2. Description of the Related Arts
Currently, hydrogen peroxide is mainly produced by the anthraquinone process. However, aqueous solutions of hydrogen peroxide produced in accordance with this process contain various kinds of inorganic impurities. Aqueous solutions of hydrogen peroxide having a substantially practical concentration, i.e., 5 to 70% by weight, generally contain several hundreds .mu.g/liter of inorganic impurities.
On the other hand, a very high purity, such as a concentration of residual inorganic impurities of several tenths .mu.g/liter or less, is required for aqueous solutions of hydrogen peroxide used in the field of semiconductor production.
Heretofore, as the process for purifying an aqueous solution of hydrogen peroxide by removing contained inorganic impurities, processes comprising bringing the aqueous solution of hydrogen peroxide into contact with an ion exchange resin have been known. It has been proposed that an aqueous solution of hydrogen peroxide is purified by using a strongly acidic cation exchange resin of a hydrogen form singly, a strongly basic anion exchange resin of a bicarbonate form, a carbonate form, or a hydroxide form singly, a mixture of a strongly acidic cation exchange resin and a strongly basic anion exchange resin, or a combination of these ion exchange resins or the mixure of ion exchange resins.
When an aqueous solution of hydrogen peroxide is purified by using an ion exchange resin, it is generally advantageous that the aqueous solution of hydrogen peroxide is brought into contact with the ion exchange resin in accordance with a continuous process in which the aqueous solution of hydrogen peroxide is passed through a column packed with the ion exchange resin. To increase the purity in accordance with this process, the time of contact of the solution with the ion exchange resin is increased. Increase in the time of contact in this process means decrease in the space velocity (SV) of the aqueous solution of hydrogen peroxide passed through the column. However, it is the real situation that decrease in the space velocity does not give rise to as much improvement in the purity as expected.